There are a number of good reasons to begin discussion of cocktails with the Old Fashioned, not the least of which being that it just happens to be my favorite drink. While many are not familiar with this drink, they may be familiar with the short glass renamed after it. Let's get right into the recipe.
The Old Fashioned
1/4-1/2 oz. simple syrup*
1-3 dashes Angostura bitters
2 oz. whiskey
Stir all three ingredients well and pour into an Old Fashioned glass filled with large ice cubes. Garnish as desired with nearly any combination of orange slice/peel, lemon peel, and/or a cherry. Please be cautious with over-garnishing your Old Fashioned. If you believe yours requires a fruit salad to be added, serve it in a separate bowl with a fork or find another drink entirely.
The whiskey selected, by tradition, should be a bourbon or a rye. I generally use bourbon, although I have been known to experiment slightly. For a while, I was crazy about Irish Old Fashioneds, made with Bushmill's. Truly, though, one can use any liquor desired, even tequila.
And depending on the size of your glass, there may be a great deal of empty space remaining. I implore you, however, not to "top off" with soda water. This heinous practice seems to have stemmed from imprecise measures of water being recommended to help muddle sugar instead of using simple syrup. This, of course, leads us to our discussion of simple syrup.
*Simple syrup (sometimes called sugar syrup or bar syrup) is nothing more than sugar dissolved in water. This serves many purposes. Most obviously, there is no need to muddle a sugar cube and teaspoon or so of water together for 45 minutes per drink to avoid the grainy texture of undissolved sugar. Secondly, depending on muddling time and technique, much of the sugar content is likely to remain at the bottom of the glass until the final sip, creating an unbalanced drink during some, if not most, of the drinking experience. Thirdly, making your own simple syrup makes you feel like a real mixologist, even though all you did was mix sugar and water ahead of time.
Simple syrup is made by heating (but not boiling) one part water and slowly stirring in an equal part of sugar until dissolved. For a rich simple syrup (what I prefer), merely double the amount of sugar used. I use a pan on the stove top, but anything that heats water will work. Once everything is dissolved, pour the syrup into an air-tight bottle (a cleaned out liquor bottle works fine) and place in the fridge or cabinet. To lengthen the time before it starts to crystallize, simply add a splash of vodka. If you'd like to experiment, a myriad of different flavors can be used.
As for the bitters, don't bother making this drink if you don't have bitters. Go out and buy some. They're dirt cheap and they're available at BevMo, some liquor stores, and several grocery stores. If you've got them, it's also quite fun to experiment with using orange bitters and/or Peychaud bitters in this drink instead of (or in addition to) the Angostura. Whatever you do, don't leave them out entirely. This cocktail illustrates the perfect balance: Whiskey to make it strong, water to make it weak, Angostura to make it bitter, and sugar to make it sweet. Along with this comes the personal balance. Everybody likes their drinks a little bit different, so I encourage you to play around a little with the measurements until you find the perfect Old Fashioned for your tastes.
If you'd like more information on the Old Fashioned, Robert Hess does an excellent job in his look at the recipe and in his in-depth look at its history. If you'd prefer to watch a video with a charming old man (who makes a fantastic cocktail), Chris McMillian should do the job nicely.